1. Field of the Invention
The present invention relates to a multipath rotary disc valve for distributing polymer plastics melts of high molecular weight.
2. Description of the Related Art
In the manufacture and processing of polymers, for achieving a flexible process it is frequently necessary to selectively distribute melt flows to different processing stages.
The distribution of melt flows of plastics having higher viscosities, for example, the distribution of polymer melts of high molecular weight, from a principal line to different distributor lines still causes technical problems today. For solving these problems, multipath valves are usually proposed in which the respective flow direction is opened or closed by pistons. For example, U.S. Pat. No. 5,211,845 describes a polymer valve in which the closing pistons are arranged in a V-shaped configuration in order to keep the dead space occurring during the exchange of the flow direction as low as possible. In connection with the alternating flow into different filter chambers, U.S. Pat. No. 5,928,523 proposes a valve construction in which three valve chambers are used which must be emptied and rinsed each time the initial positions are changed.
EP-0 962 299 A1 describes a multipath plug-type valve in which the drive is located outside of the heating unit.
These commercially available valves, such as multipath piston valves or plug-type valves, have the disadvantage that the spaces between contact surfaces and the valve chamber itself contains residues of the melt when a flow direction is closed off, wherein these residues are thermally decomposed when remaining for a long period of time at process temperature, so that carbonized decomposed products reach the polymer melt when the flow direction is used once again. In addition, sealing of the valves in piston valves can be effected only through fitted seats which are adjusted during the manufacturing process and by forcing in the plug in the case of plug-type valves. Polymer residues are also deposited in the fitted seats of piston valves, wherein these polymer residues are decomposed and reach the flow of melt when the melt is moved. Plug-type valves have the tendency to be tight to operate because of the contact pressure between surfaces which is difficult to control.
Therefore, it is the primary object of the present invention to provide a multipath valve which is free of dead space to be used for distributing melt flows in the manufacture or processing primarily of thermoplastic polymers, wherein the valve makes it possible to conduct the melt in a circulation line, directly to the output or through a casting nozzle, or which makes it possible to optionally separate or connect the valve to different melt circulations without producing melt residues.
To be able to carry out such operations as they are frequently desired in the discontinuous manufacturing processes of polymers, without the usual disadvantages of deposited, thermally decomposed melt residues in the valve chambers or in the fits required necessarily for the mobility of the closing elements, the present invention proposes a multipath valve in which the melt flows through the interior of the valve in all conditions of operation, so that the formation of melt residues is always prevented.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the descriptive matter in which there are described preferred embodiments of the invention.